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| United States Patent |
5,679,479
|
|
Young
, et al.
|
October 21, 1997
|
Battery separator
Abstract
A battery separator for use in flooded cell type lead acid batteries
comprising a backweb of a porous, acid resistant, embossable material with
a plurality of ribs extending from at least one planar surface of the
backweb. The ribs are located across the width of the backweb and extend
in a direction substantially parallel to the longitudinal dimension of the
backweb. Each rib is an embossed corrugated structure comprised of
alternating ridges and furrows. The ridges and furrows are in non-parallel
alignment to the longitudinal dimension of the separator, and preferably
perpendicular thereto. The ribs are formed on a substantially flat battery
separator backweb by passing the backweb through the nip formed by a pair
of opposed embossing rollers.
| Inventors:
|
Young; James (Sunriver, OR);
Alexander; Francis E. (Corvallis, OR)
|
| Assignee:
|
Amtek Research International LLC (Eugene, OR)
|
| Appl. No.:
|
646764 |
| Filed:
|
May 8, 1996 |
| Current U.S. Class: |
429/147; 264/284; 264/286; 429/247; 429/249 |
| Intern'l Class: |
H01M 002/16 |
| Field of Search: |
429/247,249,146,147
29/730,731
264/284,286
|
References Cited
U.S. Patent Documents
| 4000352 | Dec., 1976 | Hollenbeck et al. | 429/147.
|
| 4153759 | May., 1979 | Marata et al. | 429/147.
|
| 4228225 | Oct., 1980 | O'Rell et al. | 429/147.
|
| 4368243 | Jan., 1983 | O'Rell et al. | 429/147.
|
| 4369236 | Jan., 1983 | O'Rell et al. | 429/147.
|
| 4387144 | Jun., 1983 | McCallum et al. | 429/251.
|
| 4403024 | Sep., 1983 | Gordon et al. | 429/146.
|
| 4407063 | Oct., 1983 | Johnson | 29/623.
|
| 4482617 | Nov., 1984 | LeBayon et al. | 429/143.
|
| 4499040 | Feb., 1985 | Maemoto et al. | 264/167.
|
| 4619875 | Oct., 1986 | Stahura et al. | 429/143.
|
| 5266257 | Nov., 1993 | Kildune | 264/224.
|
Primary Examiner: Willis, Jr.; Prince
Assistant Examiner: Krueger; Jonathan S.
Attorney, Agent or Firm: Howard; Robert E.
Claims
We claim:
1. A battery separator comprising a backweb of porous, acid resistant,
embossable material, said backweb having a longitudinal dimension, a width
dimension perpendicular to said longitudinal dimension and an upper and
lower planar surface, said backweb having a plurality of embossed ribs
projecting from at least one planar surface thereof, each of said ribs
being a corrugated structure comprised of alternating ridges and furrows,
each corrugation of said corrugated structure being formed from and
integral with said embossable backweb material, each corrugation having a
sloping leading wall, a sloping trailing wall, a ridge formed where said
leading and trailing walls meet, sidewalls at the outer ends of said ridge
joined to said leading and trailing walls with the sapace enclosed by said
leading wall, trailing wall and sidewalls being hollow, said ridges and
furrows being in non-parallel alignment with said longitudinal dimension
of said backweb.
2. The battery separator of claim 1 wherein said embossable backweb
material is microporous polyethylene.
3. The battery separator of claim 1 wherein said ridges and furrows are
substantially perpendicular to the longitudinal dimension of said backweb.
4. The battery separator of claim 1 wherein said ribs extend parallel to
the longitudinal dimension of said backweb.
5. The battery separator of claim 3 wherein the frequency of said ridges is
between about 5 and about 25 per inch.
6. The battery separator of claim 1 wherein said ridges and furrows are at
an angle to the longitudinal dimension of said backweb of between about 20
degrees and about 160 degrees.
7. The battery separator of claim 6 wherein the ridges and furrows of at
least some of the ribs are at a different angle to the longitudinal
dimension of said backweb than that of the ridges and furrows of
immediately adjacent ribs.
8. The battery separator of claim 7 wherein the ridges and furrows of a
first set of ribs consisting of every other rib is at an angle to the
longitudinal dimension of said backweb of between about 20 degrees and
less than about 90 degrees and the angle of the ridges and furrows of a
second set of ribs consisting of ribs immediately adjacent said first set
of ribs is at an angle to the longitudinal dimension of said backweb of
between about 160 degrees and greater than about 90 degrees.
9. The battery separator of claim 1 wherein said ridges and furrows of at
least some of the ribs are in a chevron pattern.
10. The battery separator of claim 1 wherein said ridges and furrows of at
least some of the ribs are in a tractor tread pattern.
11. The battery separator of claim 1 wherein said ridges and furrows of at
least some of the ribs are in a continuous sinusoidal pattern.
12. A method of forming ribs on a battery separator comprising unwinding a
substantially flat web of a porous, acid resistant, embossable separator
material from a roll, said web having an upper and a lower planar surface,
feeding the web along a path and embossing said web in a plurality of
narrow lanes by subjecting at least one planar face of said web material
to plastic deformation at a plurality of embossment sites within said
lanes to form in each of said lanes a corrugated structure extending from
the other planar face of web, said corrugated structure having alternating
ridges and furrows that are non-parallel to said longitudinal edges of
said web.
13. The method of claim 12 wherein said embossing is effected by passing
the web into the nip formed by pairs of opposed embossing wheels
positioned in the locations of said narrow lanes.
14. The method of claim 12 wherein said separator material is microporous
polyethylene.
15. An apparatus for forming ribs on a battery separator web comprising a
pair of opposed rotatably mounted embossing rolls having parallel
longitudinal axes, at least one of said rolls having a plurality of
embossing wheels having a common axis with said roll located at spaced
apart embossing locations along the length of said roll, the distance
betweeen said embossing locations corresponding to the distance between
ribs to be formed on the battery separator web, and drive means for
rotating at least one of said embossing rolls.
16. The apparatus of claim 15 wherein both embossing rolls have opposed
embossing wheels.
17. The apparatus of claim 15 wherein said opposed embossing wheels
comprise gears having a plurality of intermeshing gear teeth.
Description
BACKGROUND OF THE INVENTION
This invention relates to a battery separator for use in flooded cell type
lead acid batteries and to a method and apparatus for making the
separator.
In a flooded cell type lead acid battery the positive and negative
electrodes or "plates" are separated by a battery separator. The battery
separator typically has "ribs" or protrusions extending from at least one
planar face of the separator. Such ribs are formed in one of several ways:
the ribs can be formed integrally with the backweb of the separator; the
ribs can be subsequently applied to the backweb as a bead of the same or
different material as the backweb; or the ribs can be formed by embossing
the backweb. The ribs function to provide proper spacing between the
plates and to provide a space wherein free electrolyte resides.
The battery separator currently used by most flooded cell type lead acid
battery manufacturers is of the microporous polyethylene type. This type
of separator has a composition consisting essentially of an ultra high
molecular weight polyethylene, a filler (typically amorphous silica), a
plasticizer (typically a processing oil), and certain minor ingredients
such as an antioxidant, lubricant and carbon black.
Microporous polyethylene separator material is commercially manufactured by
passing the ingredients through a heated extruder, passing the extrudate
generated by the extruder through a die and into the nip formed by two
heated calender rolls to form a continuous web, extracting a substantial
amount of the processing oil from the web by use of a solvent, drying the
extracted web, slitting the web into lanes of predetermined width, and
winding the lanes into rolls.
Such separators and a method of manufacturing them are described in U.S.
Pat. No. 3,351,495.
Microporous polyethylene separators typically have a configuration
comprising a backweb having a predetermined thickness, and a plurality of
parallel ribs spaced apart a predetermined distance and extending
outwardly from one planar surface of the backweb. The ribs extend
continuously in a longitudinal direction parallel to the edges of the
separator material. A partial perspective view of such a prior art
separator is illustrated in FIG. 7. The thickness of the backweb and
height and spacing of the ribs is specified to the separator manufacturer
by the battery manufacturer; the specifications are designed to maximize
certain battery characteristics desired by the battery manufacturer.
Such ribs are formed during manufacture of the microporous polyethylene
separator by providing that one of the two heated calender rolls forming
the nip through which the extrudate from the extruder is fed is engraved
with grooves so that the ribs are formed as an integral part of the
separator web.
There are many different specifications required by battery manufacturers
relative to rib size and rib spacing. In manufacturing separator material
to meet customer requirements, almost every change in rib size and spacing
requires that the separator manufacturer shut down its manufacturing line
in order to remove the engraved roll that had been in use to fill the
prior order and to insert a differently configured engraved roll capable
of producing the rib size and spacing required for the new order to be
filled. Manufacturing time is lost during such shut-down and extra scrap
material is generated during start-up of the line.
In addition, integrally formed ribs in the polyethylene type separator
undergoes extraction along with the backweb and, because it has relatively
more volume than a portion of the backweb occupying the same planar
surface area, generally the ribs retain more processing oil than the
backweb, thereby raising the overall electrical resistance of the
separator.
It is an object of this invention to provide a separator having a new type
of rib formed thereon that occupies less volume of the separator but
provides at least as good spacing ability between plates as prior art
ribs.
It is a further object of this invention to provide a battery separator
having a rib configuration that is capable of being formed on the
separator subsequent to formation of the backweb.
It is a further object of this invention to provide a simple method and
apparatus for forming the ribs on such separators.
SUMMARY OF THE INVENTION
This invention relates to a battery separator having a longitudinal
dimension, a width dimension perpendicular to said longitudinal dimension,
upper and lower planar faces, and a plurality of ribs (at least three)
projecting from at least one planar face, said ribs extending in a
direction substantially parallel to the longitudinal dimension of the
separator, each of the ribs being formed of a plurality of individual
projecting embossments forming a corrugated structure comprised of
alternating ridges and furrows.
It is preferred to have ribs extending from both planar faces of the
separator. In this preferred mode adjacent projecting embossments (ridges)
on one planar face are separated by an indentation (furrow) which forms a
projecting embossment (ridge) on the other planar face of the separator.
Where ribs extend from both planar faces of the separator, the ribs
projecting from one planar surface may have a height equal to or different
from the height of the ribs extending from the other planar surface.
This invention also relates to a method and apparatus for forming ribs in a
substantially flat separator web having a longitudinal dimension, a width
dimension perpendicular to the longitudinal dimension and upper and lower
planar faces by passing a substantially continuous web of such material
between a plurality of sets of aligned embossing wheels, each of the sets
of aligned embossing wheels forming a single rib, adjacent sets of wheels
being spaced apart by the distance desired between the ribs, each of the
sets of aligned embossing wheels forming a plurality of embossments in the
web of separator material in the longitudinal direction of the web.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial perspective view of the upper planar surface of the
separator material of this invention.
FIG. 2 is an enlarged partial edge view in cross-section of the separator
taken along line 2--2 of FIG. 1.
FIG. 3 is an enlarged partial edge view in cross-section of a separator rib
taken along line 3--3 of FIG. 1.
FIG. 4 is an enlarged partial top plan view of a single rib of this
invention.
FIG. 5 is a frontal view of two embossing rolls employing a plurality of
embossing wheels.
FIG. 6 is a side view of two adjacent embossing wheels.
FIG. 7 is a perspective view of a portion of a prior art separator showing
the backweb and integrally formed ribs extending from the backweb.
FIGS. 8 through 11 are partial top plan views of the upper planar surface
of the separator illustrating several alternative configurations for the
rib configuration.
DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 is a partial perspective top view of the separator of this
invention. Projecting from the upper planar surface 12 of separator 10 are
a plurality of ribs 14a through 14j. The ribs 14 are disposed in narrow
lanes in the longitudinal direction of the separator 10, substantially
parallel to longitudinal edges 16 and 18 thereof.
FIG. 2 is a partial edge view in cross-section of separator 10 taken along
Line 2--2 of FIG. 1. Rib 14 projects above upper planar surface 12 of
backweb 20 of separator 10. Projecting below lower planar surface 13 of
backweb 20 is a rib 15. Ribs 14 and 15 are identical in width and lie in
the same vertical plane.
A partial edge view in cross-section of ribs 14 and 15 is illustrated in
FIG. 3. As can be seen, rib 14 is a corrugated structure comprised of
alternating ridges and furrows 22a and 23a, 22b and 23b, 22c and 23c, 22d
and 23d, etc., respectively. Likewise, rib 15 is a corrugated structure
comprised of alternating ridges and furrows 24a and 25a, 24b and 25b, 24c
and 25c, 24d and 25d, etc., respectively. A ridge on one planar surface
forms the furrow on the other planar surface, and vice versa. For example,
the underside of ridge 22a of rib 14 forms the furrow 25a of rib 15.
FIG. 4 is an enlarged, partial top view of a rib 14. As can be seen, ridges
22 and furrows 23 of rib 14 are perpendicular to the longitudinal side
walls 26 and 28 of rib 14 and thus also perpendicular to the
longitudinally disposed side edges 16 and 18 of separator 10.
The length dimension of the ridges 22 and 24, i.e., the length of the
ridges 22 and 24 from one side wall 26 to the other side wall 28 of rib
14, is selected in accordance with the desired width of the narrow lanes
constituting the ribs. This dimension will generally be between about
0.020 and about 0.060 inch.
The frequency of the ridges, i.e., the number of ridges per unit of rib
length, will preferably be between about 5 and about 25 ridges per inch.
The height of the ridges 22 and 24 above the respective planar surfaces 12
and 13 of the backweb 20 is selected in accordance with the desired height
of the ribs. This dimension will generally be between about 0.01 to about
0.10 inch.
The distance between adjacent ribs will generally be between about 0.25 to
about 1.0 inch.
The width of the separator of this invention can be any width used by
battery manufacturers; generally this width will range between about 2 to
about 12 inches.
The thickness of backweb 20 of the separator 10 will typically range
between about 0.002 to about 0.025 inch.
The cross-section of the corrugated structure forming the rib of this
invention is illustrated in FIGS. 1-4 as being triangular, with each
individual embossed projection thus being wedge shaped. Each wedge shaped
embossment is comprised of a sloping leading wall 17, a sloping trailing
wall 19 and vertical side walls 26 and 28. However, other similar wedge
shapes may be use, including but not limited to a rounded wedge shape
where the ridge is slightly rounded instead of angular, or a flattened
wedge shape where the ridge is either formed flat during embossing or the
ridge flattened by subsequent pressing.
One of the advantages obtained in using the separator of the present
invention is that, since the ribs are a corrugated structure formed of
adjacent ridges and furrows, the separator provides a substantially
barrier free environment for flow of electrolyte and any gases released
during charging and discharging since the ribs contact the plates only in
the ridge area. Prior art ribs (see, for example, FIG. 7), being sold, are
in contact with the positive plate in the entire upper surface area of the
rib which imposes a barrier to electrolyte and/or gas flow.
A further advantage obtained in using the separator of the present
invention is in reducing or eliminating rib bending and/or flattening. In
assembling a battery the number of alternating enveloped (with separator
material) and unenveloped plates required to form a cell are stacked
together, compressed and inserted into a cell compartment of a battery
case. The compressive forces to which the separators are subjected can
cause undesirable rib bending and/or flattening with conventional rib
construction, especially at higher "overall" dimensions, i.e., rib
heights. The rib configuration of the present invention reduces or
eliminates such rib bending and/or flattening. Although the separator of
the invention is illustrated as having ribs 14 and 15 extending from both
planar surfaces 12 and 13 of the backweb 20, the invention is intended to
include a separator where the ribs are formed on only one side. Similarly,
although the ribs 14 and 15 are illustrated as having the same height
above planar surfaces 12 and 13, respectively, of backweb 20, the height
of the ribs on one side may be greater or lesser than the height of the
ribs on the other side.
In addition, adjacent ridges of a rib may vary in height. FIGS. 5 and 6
illustrate an apparatus suitable for making the separators of this
invention. FIG. 5 is a front view of two embossing rolls 30 and 32 having
a plurality of embossing wheels 31a-31g and 33a-33g, respectively, located
thereon. Each of embossing wheels 31a-31g on embossing roll 30 are aligned
with embossing wheels 33a-33g, respectively, on embossing roll 32. Each of
the embossing wheels 31 and 33 are, essentially, gear wheels with a
plurality of gear teeth 32 and 33, respectively, projecting therefrom, as
best seen in FIG. 6. The phrase "embossing wheels" is intended to include
both separate gear wheels located on an embossing roll or axle (such as by
press fitting) or an embossing roll having multiple rows of teeth machined
therein.
Embossing rolls 30 and/or 32 are rotated by suitable drive means, not
shown. It is preferred to have only one of embossing rolls 30 or 32 driven
by external drive means with the other roll being rotated by the driven
embossing roll. The gear teeth 32 and 34 of aligned embossing wheels 31
and 33 intermesh and emboss ribs 14 and 15 into flat separator material 20
when it is passed through the nip between rotating embossing rolls 30 and
32 in the direction indicated by the arrow in FIG. 6.
Where the height of the ribs extending from both planar faces are the same,
the teeth 32 and 34 are equal in height.
Where the height of the ribs one side is different than the height of the
ribs on the other side, the height of gear teeth 32 and 34 are,
correspondingly, different in height.
Where it is desired to have ribs extending from only one surface of the
separator, one of embossing wheels 31 or 33 may be a "male" roll having
gear teeth as illustrated with the other embossing wheel being a "female"
roll having grooves therein with dimensions corresponding to the
dimensions of the gear teeth extending from the male roll.
Where it is desired to have a rib where adjacent ridges have different
heights above the adjacent planar surface of the separator backweb this
may be achieved by using as the first embossing roll a male with gear
teeth of varying height and as the second embossing roll a smooth roll
formed of rubber or other deformable material.
The formation of the ribs of the present invention involves plastic
deformation of the backweb material in the plurality of narrow lanes where
the embossing takes place. Permanent deformation indicates that the
material was loaded beyond its yield point which, by definition, means
that it has experienced plastic flow. It has been shown that oxidation
resistance is improved in the area of plastic deformation due to oil being
driven to the surface upon collapse of micropores.
FIG. 7 is a perspective view of a prior art separator 40 having a plurality
of ribs 42 extending from the upper planar face 44 of backweb 46. Ribs 42
are integral with backweb 46 and are formed during the calendering of
extrudate, as described above in the discussion of the background
material. In the preferred mode of practicing the present invention the
web upon which ribs are formed is flat on both sides and constitutes the
backweb 20 of the finished separator 10. However, it is intended to
include within the definition of "flat" or "substantially flat" (as used
herein) a web having some minor ribs formed therein during the calendering
phase of its manufacture.
Although the invention has been described relative to forming ribs in a
microporous polyethylene separator, as this is the principal type of
separator material currently used by flooded cell type lead acid battery
manufacturers, any separator material which is porous, acid resistant and
capable of being permanently embossed may be used. These materials may be
generally characterized as filled or unfilled films and nonwoven webs of
thermoplastic or thermoset polymers. Suitable thermoplastic polymers
include polymers and copolymers of ethylene, propylene, butylene, vinyl
chloride and styrene. Suitable thermoset compositions include phenolics,
ethylene/propylene/diene, isoprene, butadiene, styrene and similar
thermosetting polymers.
The ribs have been illustrated in the preferred embodiment disclosed herein
as having ridges and furrows that are perpendicularly aligned with the
longitudinal dimension of the separator. However, the alignment of the
ridges and furrows may be such as to form an angle to the longitudinal
dimension of the separator, such angle being less than 180 degrees, and
preferably less than about 160 degrees, to the longitudinal dimension, but
greater than 0 degrees and preferably greater than about 20 degrees. In
addition, the alignment of the ridges and furrows of some ribs to the
longitudinal dimension of the separator may vary from the alignment of the
ridges and furrows of other ribs.
Examples of such alternative configurations are illustrated in FIGS. 8-11.
FIG. 8 illustrates a separator 100 in which the ribs 114 have embossments
in adjacent ribs 114a, 114b and 114c whose ridges 122 and 124, and
corresponding furrows, are alternatingly angled with respect to each
other.
FIG. 9 illustrates a separator 200 in which the ridges of rib 214 form a
chevron pattern made up of ridge elements 222 and 224.
FIG. 10 illustrates a separator 300 in which the ridges of rib 314 form a
tractor tread pattern made up of ridge elements 322 and 324.
FIG. 11 illustrates a separator 400 in which the ridges of rib 414 form a
continuous sinusoidal (zig-zag) pattern made up of ridge elements 422 and
424. The continuous sinusoidal pattern of the ridges could be rounded ("S"
shaped) instead of sharp as illustrated in FIG. 11.
A primary advantage of the present invention is that it allows battery
separator manufacturers to continuously produce a substantially flat sheet
of microporous material without interrupting the manufacturing process to
change engraved calender rolls. Such flat sheet would then be supplied to
the battery manufacturer in rolls of appropriate width and the battery
manufacturer would apply the ribs in accordance with this invention. It is
contemplated that such ribs would be applied just prior to the plate
enveloping operation.
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